2 INTRODUCTION. 



Monograph that Van Tieghem in 1880 and Bivfeld in 1884 corrected 

 this view. Accepting the Mycetozoa as established by Rostafinski, 

 but excluding Dictyostelium on the ground of its not forming a 

 true plasniodiuin, we have a clearly defined group of organisms 

 separated from all others by the following combination of 

 characters. A spore provided with a firm wall produces on 

 germination an amoeboid swarm-cell which soon acquires a 

 flagellum. The swarm-cells multiply by division and subsequently 

 coalesce to form a plasmodium which exhibits a rhythmic 

 streaming. The plasmodium gives rise to fruits which consist 

 of supporting structures and spores ; in the JEndosporece these 

 have the form of sporangia, each having a wall within which 

 the free spores are developed. A capillitium or system of threads 

 forming a scaffolding among the spores is present in most genera. 

 In the Exosporece the fruits consist of sporophores bearing numer- 

 ous spores on their surface. 



The Spore and Swarm-cell. - r h& spores of the Endosporece are 

 mostly spherical, but occasionally they are ellipsoid. Their size 

 is uniform in each species, or with so little variation that their 

 measurement affords a valuable character for specific determination. 

 This is not without exception ; for instance, in the abundant 

 species Leocarpus fragilis the spores are commonly 11 to 12 /a, 

 diameter, but in occasional gatherings they average 16 to 20 /x. 

 In other genera which present ample material for comparison, 

 similar variation is sometimes met with. The spore- wall 

 is variously coloured in the different species. It is described 

 by Zopf as showing the chemical reaction of cellulose, and 

 consisting of a simple firm membrane ; * but the spores of several 

 species of Didymium and Frichia, when crushed in an acetic 

 solution of gentian-violet, show the existence of two layers, the 

 inner more delicate and appearing less deeply stained than the 

 outer. In Physarum, Arcyria, and genera with thin-walled 

 spores, the double layer has not been traced. It is either 

 smooth or marked with sculpture. The contents of the spore 

 consists of faintly granular protoplasm with a single central 

 nucleus. In abnormal developments, monstrous spores, often of 

 irregular shape and containing several nuclei, are of frequent 

 occurrence. 



The length of time that elapses before the germination of the 

 spore after it has been placed in water varies with the species, 

 and often in different gatherings of the same species. In the 

 darker spores of Stemonitis fusca it does not begin for nine or 

 twelve hours, while in the pale-spored variety it has been 

 observed to occur in twenty-eight minutes. In Reticularict 

 Lycoperdon it usually takes place in less than an hour in fresh 

 gatherings ; spores from a specimen which had been stored for 

 nearly three years began to germinate in four hours, and in 

 twenty hours nearly every spore had done so. Didymium diffbrme 



* Schenk, "Hantlbuch dor Botanik," Bd. iii. 2, 1881 ; "Die Pilztliiere," 

 p. 53. 



